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2003-07-10
|
Continuous Measurement of Atom-Number Moments of a Bose-Einstein Condensate by Photodetection
|
We propose a measurement scheme that allows determination of even-moments of
a Bose-Einstein condensate (BEC) atom number, in a ring cavity, by continuous
photodetection of an off-resonant quantized optical field. A fast cavity
photocounting process limits the heating of atomic samples with a relatively
small number of atoms, being convenient for BECs on a microchip scale
applications. The measurement back-action introduces a counting-conditioned
phase damping, suppressing the condensate typical collapse and revival
dynamics.
|
0307221v3
|
2003-07-18
|
Dynamics of a nanoparticle as a one-spin system and beyond
|
We review some recent results beyond the now established theory of
magnetization switching of a nanoparticle within the single-spin approximation.
The first extension is that of the Stoner-Wohlfarth model for magnetization
static switching under applied magnetic field including the effect of
temperature at long-time scales. The second concerns a generalization of the
N\'eel-Brown model for thermoactivated dynamic magnetization switching to
include the effect of exchange interaction in the framework of Langer's theory
in the intermediate-to-high damping limit. We finally argue why the single-spin
approximation is not appropriate for very small nanoparticles.
|
0307457v1
|
2003-07-21
|
Rate description of Fokker-Planck processes with time dependent parameters
|
The reduction of a continuous Markov process with multiple metastable states
to a discrete rate process is investigated in the presence of slow time
dependent parameters such as periodic external forces or slowly fluctuating
barrier heights. A quantitative criterion is provided under which condition a
kinetic description with time dependent frozen rates applies. Finally it is
shown how the long time behavior of the underlying continuous process can be
retrieved from the knowledge of the discrete process by means of an appropriate
random decoration of the discrete states. As a particular example of the
presented theory an over-damped bistable Brownian oscillator with periodic
driving is discussed.
|
0307498v1
|
2003-09-12
|
Intersubband plasmons in quasi-one-dimensional electron systems on a liquid helium surface
|
The collective excitation spectra are studied for a multisubband
quasi-one-dimensional electron gas on the surface of liquid helium. Different
intersubband plasmon modes are identified by calculating the spectral weight
function of the electron gas within a 12 subband model. Strong intersubband
coupling and depolarization shifts are found. When the plasmon energy is close
to the energy differences between two subbands, Landau damping in this finite
temperature system leads to plasmon gaps at small wavevectors.
|
0309323v1
|
2003-10-06
|
Phonons in an Inhomogeneous Continuum: Vibrations of an Embedded Nanoparticle
|
The spectrum of acoustic vibrational modes of an inhomogeneous elastic
continuum are analyzed with application to a spherical nanoparticle embedded in
an infinite glass block. The relationship of these modes to the discrete
vibrational spectrum of a free sphere is studied. The vibrational modes of a
sphere with a fixed surface are relevant in some situations. Comparisons are
also made to calculations of mode frequency and damping based on complex valued
frequency.
|
0310099v5
|
2003-10-16
|
Sorting by Periodic Potential Energy Landscapes: Optical Fractionation
|
Viscously damped objects driven through a periodically modulated potential
energy landscape can become kinetically locked in to commensurate directions
through the landscape, and thus can be deflected away from the driving
direction. We demonstrate that the threshold for an object to become
kinetically locked in to an array can depend exponentially on its size. When
implemented with an array of holographic optical tweezers, this provides the
basis for a continuous and continuously optimized sorting technique for
mesoscopic objects called ``optical fractionation''.
|
0310396v1
|
2003-11-18
|
Quantum-critical behavior of itinerant ferromagnets
|
We study the stability of the Quantum Critical Point (QCP) for itinerant
ferromagnets commonly described by the Hertz-Millis-Moriya (HMM) theory. We
argue that in $D \leq 3$, long-range spatial correlations associated with the
Landau damping of the order parameter field generate a universal {\it
negative}, non-analytic $|q|^{(D+1)/2}$ contribution to the static magnetic
susceptibility $\chi_s (q, 0)$, which makes HMM theory unstable. We argue that
the actual transition is either towards incommensurate ordering, or first
order. We also show that singular corrections are specific to the spin problem,
while charge susceptibility remains analytic at criticality.
|
0311420v1
|
2003-11-24
|
Simulating spin-boson dynamics with stochastic Liouville-von Neumann equations
|
Based on recently derived exact stochastic Liouville-von Neumann equations,
several strategies for the efficient simulation of open quantum systems are
developed and tested on the spin-boson model. The accuracy and efficiency of
these simulations is verified for several test cases including both coherent
and incoherent dynamics, involving timescales differing by several orders of
magnitude. Using simulations with a time-dependent field, the time evolution of
coherences in the reduced density matrix is investigated. Even in the case of
weak damping, pronounced preparation effects are found. These indicate hidden
coherence in the interacting system which can only be indirectly observed in
the basis of the reduced quantum dynamics.
|
0311544v1
|
2003-12-12
|
Interaction-induced dephasing of Aharonov-Bohm oscillations
|
We study the effect of the electron-electron interaction on the amplitude of
mesoscopic Aharonov-Bohm oscillations in quasi-one-dimensional (Q1D) diffusive
rings. We show that the dephasing length L_phi^AB governing the damping factor
exp(-2piR / L_phi^AB) of the oscillations is parametrically different from the
common dephasing length for the Q1D geometry. This is due to the fact that the
dephasing is governed by energy transfers determined by the ring circumference
2piR, making L_phi^AB R-dependent.
|
0312325v2
|
2004-01-21
|
Non-fermi liquid behavior in itinerant antiferromagnets
|
We consider a two dimensional itinerant antiferromagnet near a quantum
critical point. We show that, contrary to conventional wisdom, fermionic
excitations in the ordered state are not the usual Fermi liquid quasiparticles.
Instead, down to very low frequencies, the fermionic self energy varies as
$\omega^{2/3}$. This non-Fermi liquid behavior originates in the coupling of
fermions to the longitudinal spin susceptibility $\chi_{\parallel}(q, \Omega)$
in which the order-induced ``gap'' in the spectrum at $q=0$ dissolves into the
Landau damping term at $v_F q >\Omega$. The transverse spin fluctuations obey
$z=1$ scaling characteristic of spin waves, but remain overdamped in a finite
range near the critical point.
|
0401375v1
|
2004-02-05
|
Oscillations of atomic fermions in a one dimensional optical lattice
|
A semiclassical model is used to investigate oscillations of atomic fermions
in a combined magnetic trap and one dimensional optical lattice potential
following axial displacement of the trap. The oscillations are shown to have a
characteristic small amplitude, damped behavior in the collisionless regime.
The presence of a separatrix in the semiclassical Brillouin zone phase space is
predicted and shown to produce a strongly asymmetric phase space distribution
function.
|
0402166v1
|
2004-02-20
|
Low-frequency incommensurate magnetic response in strongly correlated systems
|
It is shown that in the t-J model of Cu-O planes at low frequencies the
dynamic spin structure factor is peaked at incommensurate wave vectors
(1/2+-delta,1/2)$, (1/2,1/2+-delta). The incommensurability is connected with
the momentum dependencies of the magnon frequency and damping near the
antiferromagnetic wave vector. The behavior of the incommensurate peaks is
similar to that observed in La_{2-x}(Ba,Sr)_xCuO_{4+y} and YBa_2Cu_3O_{7-y}:
for hole concentrations 0.02<x<=0.12 we find that delta is nearly proportional
to x, while for x>0.12 it tends to saturation. The incommensurability
disappears with increasing temperature. Generally the incommensurate magnetic
response is not accompanied by an inhomogeneity of the carrier density.
|
0402512v1
|
2004-02-20
|
Umklapp collisions and center of mass oscillation of a trapped Fermi gas
|
Starting from the the Boltzmann equation, we study the center of mass
oscillation of a harmonically trapped normal Fermi gas in the presence of a
one-dimensional periodic potential. We show that for values of the the Fermi
energy above the first Bloch band the center of mass motion is strongly damped
in the collisional regime due to umklapp processes. This should be contrasted
with the behaviour of a superfluid where one instead expects the occurrence of
persistent Josephson-like oscillations.
|
0402532v2
|
2004-03-01
|
Raman scattering on phonon-plasmon coupled modes in magnetic fields
|
Raman scattering on phonon--plasmon coupled modes in high magnetic fields is
considered theoretically. The calculations of the dielectric function were
performed in the long-wave approximation for the semiclassical and
ultra-quantum magnetic fields taking into account the electron damping and
intrinsic lifetime of optical phonons. The Raman scattering has resonances at
the frequencies of coupled modes as well as at multiples of the cyclotron
frequency. The dependence of the Raman cross section on the carrier
concentration is analyzed.
|
0403044v1
|
2004-03-02
|
Ferromagnetic EuS films: Magnetic stability, electronic structure and magnetic surface states
|
We present the temperature and layer dependent electronic structure of a
20-layer EuS(100)-film using a combination of first-principles and model
calculation, the latter based on the ferromagnetic Kondo-lattice. The
calculated thickness-dependent Curie temperature agrees very well with
experimental data. The projected 5d-bandstructure is at finite temperatures
strongly influenced by damping effects due to spin exchange processes.
Spin-split unoccupied 5d-surfaces states are found with a Stoner-like
collapsing for increasing temperature towards the Curie point and with an
exponential decay of spectral weight with increasing distance from the surface.
|
0403075v1
|
2004-03-05
|
BCS pairing in Fermi systems with several flavors
|
Motivated by the prospect of Bardeen-Cooper-Schrieffer (BCS) pairing in cold
fermionic gases we analyze the superfluid phase of 3 fermionic flavors in the
attractive Hubbard model. We show that there are several low--lying collective
pairing modes and investigate their damping due to the partially gapless nature
of the single-particle spectrum. Furthermore we analyze how these modes show up
in the density response of the system. Apart from the Anderson-Bogoliubov phase
mode of the pairing between two flavors, the dynamical structure factor
contains signatures of the gapless third flavor. This picture is found to be
robust against perturbations that break the global SU(3)-symmetry of the
Hamiltonian.
|
0403166v1
|
2004-03-17
|
Quantum transport of non-interacting Fermi gas in an optical lattice combined with harmonic trapping
|
We consider a non-interacting Fermi gas in a combined harmonic and periodic
potential. We calculate the energy spectrum and simulate the motion of the gas
after sudden replacement of the trap center. For different parameter regimes,
the system presents dipole oscillations, damped oscillations around the
replaced center, and localization. The behaviour is explained by the change of
the energy spectrum from linear to quadratic.
|
0403429v2
|
2004-03-28
|
A Josephson junction as a detector of Poissonian charge injection
|
We propose a scheme of measuring the non-Gaussian character of noise by a
hysteretic Josephson junction in the macroscopic quantum tunnelling (MQT)
regime. We model the detector as an (under)damped $LC$ resonator. It transforms
Poissonian charge injection into current through the detector, which samples
the injection statistics over a floating time window of length $\sim Q/\omega
_{\rm J}$, where $Q$ is the quality factor of the resonator and $\omega_{\rm
J}$ its resonance frequency. This scheme ought to reveal the Poisson character
of charge injection in a detector with realistic parameters.
|
0403673v1
|
2004-04-01
|
A Molecular Matter-Wave Amplifier
|
We describe a matter-wave amplifier for vibrational ground state molecules,
which uses a Feshbach resonance to first form quasi-bound molecules starting
from an atomic Bose-Einstein condensate. The quasi-bound molecules are then
driven into their stable vibrational ground state via a two-photon Raman
transition inside an optical cavity. The transition from the quasi-bound state
to the electronically excited state is driven by a classical field.
Amplification of ground state molecules is then achieved by using a strongly
damped cavity mode for the transition from the electronically excited molecules
to the molecular ground state.
|
0404006v2
|
2004-05-28
|
Shot Noise of a Tunnel Junction Displacement Detector
|
We study quantum-mechanically the frequency-dependent current noise of a
tunnel-junction coupled to a nanomechanical oscillator. The cases of both DC
and AC voltage bias are considered, as are the effects of intrinsic oscillator
damping. The dynamics of the oscillator can lead to large signatures in the
shot noise, even if the oscillator-tunnel junction coupling is too weak to
yield an appreciable signature in the average current. Moreover, the
modification of the shot noise by the oscillator cannot be fully explained by a
simple classical picture of a fluctuating conductance.
|
0405687v1
|
2004-06-22
|
Time domain analysis of dynamical switching in a Josephson junction
|
We have studied the switching behaviour of a small capacitance Josephson
junction both in experiment, and by numerical simulation of a model circuit.
The switching is a comples process involving the transition between two
dynamical states of the non-linear circuit, arising from a frequency dependent
damping of the Josephson junction. We show how a specific type of bias
pulse-and-hold, can result in a fast detection of switching, even when the
measurement bandwidth of the junction voltage is severely limited, and/or the
level of the switching current is rather low.
|
0406510v1
|
2004-07-28
|
Macroscopic quantum effects in a strongly driven nanomechanical resonator
|
We investigate the nonlinear response of a vibrating suspended nanomechanical
beam on external periodic driving. The amplitude of the fundamental transverse
mode behaves thereby like a weakly damped quantum particle in a driven
anharmonic potential. Upon using a Born-Markovian master equation, we calculate
the fundamental mode amplitude for varying driving frequencies. In the
nonlinear regime, we observe resonances which are absent in the corresponding
classical model. They are shown to be associated with resonant multi-phonon
excitations.
Furthermore, we identify resonant tunneling in a dynamically induced bistable
effective potential.
|
0407720v2
|
2004-09-09
|
Microwave photoresponse in the 2D electron system caused by intra-Landau level transitions
|
The influence of microwave radiation on the DC-magnetoresistance of
2D-electrons is studied in the regime beyond the recently discovered zero
resistance states when the cyclotron frequency exceeds the radiation frequency.
Radiation below 30 GHz causes a strong suppression of the resistance over a
wide magnetic field range, whereas higher frequencies produce a non-monotonic
behavior in the damping of the Shubnikov-de Haas oscillations. These
observations are explained by the creation of a non-equilibrium electron
distribution function by microwave induced intra-Landau level transitions.
|
0409228v1
|
2004-09-14
|
Thermal fluctuations and longitudinal relaxation of single-domain magnetic particles at elevated temperatures
|
We present numerical and analytical results for the swiching times of
magnetic nanoparticles with uniaxial anisotropy at elevated temperatures,
including the vicinity of T_c. The consideration is based in the
Landau-Lifshitz-Bloch equation that includes the relaxation of the
magnetization magnitude M. The resulting switching times are shorter than those
following from the naive Landau-Lifshitz equation due to (i) additional barrier
lowering because of the reduction of M at the barrier and (ii) critical
divergence of the damping parameters.
|
0409344v1
|
2004-09-21
|
Quantum and Classical Dissipative Effects on Tunnelling in Quantum Hall Bilayers
|
We discuss the interplay between transport and dissipation in quantum Hall
bilayers. We show that quantum effects are relevant in the pseudospin picture
of these systems, leading either to direct tunnelling currents or to quantum
dissipative processes that damp oscillations around the ground state. These
quantum effects have their origins in resonances of the classical spin system.
|
0409547v2
|
2004-09-24
|
Viscous relaxation and collective oscillations in a trapped Fermi gas near the unitarity limit
|
The viscous relaxation time of a trapped two-component gas of fermions in its
normal phase is calculated as a function of temperature and scattering length,
with the collision probability being determined by an energy-dependent s-wave
cross section. The result is used for calculating the temperature dependence of
the frequency and damping of collective modes studied in recent experiments,
starting from the kinetic equation for the fermion distribution function with
mean-field effects included in the streaming terms.
|
0409660v2
|
2004-11-02
|
Spin dynamics in the stripe phase of the cuprates
|
Within a model that supports stripe spin and charge order coexisting with a
d$_{x^2-y^2}$-wave superconducting phase, we study the self-consistently
obtained electronic structure and the associated transverse dynamical spin
susceptibility. In the coexisting phase of superconducting and static stripe
order, the resulting particle-hole continuum can strongly damp parts of the
low-energy spin wave branches. This provides insight into recent inelastic
neutron scattering data revealing the dispersion of the low-energy collective
magnetic modes of lanthanum based cuprate superconductors.
|
0411065v1
|
2004-11-05
|
Zero sound in a single component fermion - Bose Einstein Condensate mixture
|
The resonant dynamics of mediated interactions supports zero-sound in a cold
atom degenerate mixture of a single component fermion gas and a Bose-Einstein
condensate (BEC). We characterize the onset of instability in the phase
separation of an unstable mixture and we find a rich collective mode structure
for stable mixtures with one undamped mode that exhibits an avoided crossing
and a Landau-damped mode that terminates.
|
0411125v1
|
2004-11-19
|
Vortex motion rectification in Josephson junction arrays with a ratchet potential
|
By means of electrical transport measurements we have studied the rectified
motion of vortices in ratchet potentials engineered on over-damped Josephson
junction arrays. The rectified voltage as a function of the vortex density
shows a maximum efficiency close a matching condition to the period of the
ratchet potential indicating a collective vortex motion. Vortex current
reversals where detected varying the driving force and vortex density revealing
the influence of vortex-vortex interaction in the ratchet effect.
|
0411507v1
|
2004-12-07
|
A Bose-Einstein condensate in a random potential
|
An optical speckle potential is used to investigate the static and dynamic
properties of a Bose-Einstein condensate in the presence of disorder. For
strong disorder the condensate is localized in the deep wells of the potential.
With smaller levels of disorder, stripes are observed in the expanded density
profile and strong damping of dipole and quadrupole oscillations is seen.
Uncorrelated frequency shifts of the two modes are measured for a weak disorder
and are explained using a sum-rules approach and by the numerical solution of
the Gross-Pitaevskii equation.
|
0412167v1
|
2005-01-05
|
Full counting statistics of strongly non-Ohmic transport through single molecules
|
We study analytically the full counting statistics of charge transport
through single molecules, strongly coupled to a weakly damped vibrational mode.
The specifics of transport in this regime - a hierarchical sequence of
avalanches of transferred charges, interrupted by "quiet" periods - make the
counting statistics strongly non-Gaussian. We support our findings for the
counting statistics as well as for the frequency-dependent noise power by
numerical simulations, finding excellent agreement.
|
0501065v2
|
2005-01-11
|
The kinetic Monte Carlo Simulation scheme of the homoepicaxial growth of GaAs(001) for heterostructural growth on GaAs(001) substrate
|
The simulation scheme for heterostructural growth of compound semiconductors
is presented based on the kinetic Monte Carlo method. The sheme is designed as
simple as possible in order to apply it for any heteroepitaxial growth on
GaAs(001) substrate. The parameters used in the simulation are determined with
the first-principles calculation to reproduce experimental RHEED intensity
curves for homoepitaxial growth of GaAs(001).
|
0501233v1
|
2005-01-13
|
Magnetization noise in magnetoelectronic nanostructures
|
By scattering theory we show that spin current noise in normal electric
conductors in contact with nanoscale ferromagnets increases the magnetization
noise by means of a fluctuating spin-transfer torque. Johnson-Nyquist noise in
the spin current is related to the increased Gilbert damping due to spin
pumping, in accordance with the fluctuation-dissipation theorem. Spin current
shot noise in the presence of an applied bias is the dominant contribution to
the magnetization noise at low temperatures.
|
0501318v1
|
2005-01-19
|
Ferromagnetic 0-pi Junctions as Classical Spins
|
The ground state of highly damped PdNi based 0-pi ferromagnetic Josephson
junctions shows a spontaneous half quantum vortex, sustained by a supercurrent
of undetermined sign. This supercurrent flows in the electrode of a Josephson
junction used as a detector and produces a phi(0)/4 shift in its magnetic
diffraction pattern. We have measured the statistics of the positive or
negative sign shift occurring at the superconducting transition of such a
junction. The randomness of the shift sign, the reproducibility of its
magnitude and the possibility of achieving exact flux compensation upon field
cooling: all these features show that 0-pi junctions behave as classical spins,
just as magnetic nanoparticles with uniaxial anisotropy.
|
0501459v1
|
2005-02-11
|
Self-generated locality near a ferromagnetic quantum-critical point
|
We analyze the behavior of interacting fermions near a ferromagnetic
Stoner instability.
We show that the Landau damping of the spin susceptibility is a relevant
perturbation near a ferromagnetic quantum-critical point (FQCP). We argue that,
as the system approaches a FQCP, the fermionic self-energy crosses over from
predominantly momentum dependent away from the transition to predominantly
frequency dependent in the immediate vicinity of the transition. We argue that
due to this self-generated locality, the quasiparticle effective mass does not
diverge before a FQCP is reached.
|
0502302v1
|
2005-02-23
|
Microscopic analysis of the coherent optical generation and the decay of charge and spin currents in semiconductor heterostructures
|
The coherent optical injection and temporal decay of spin and charge currents
in semiconductor heterostructures is described microscopically, including
excitonic effects, carrier LO-phonon and carrier-carrier scattering, as well as
nonperturbative light-field-induced intraband and interband excitations. A
nonmonotonous dependence of the currents on the intensities of the laser beams
is predicted. Enhanced damping of the spin current relative to the charge
current is obtained as a consequence of spin-dependent Coulomb scattering.
|
0502557v1
|
2005-02-24
|
Disentangling instrumental broadening
|
A new procedure aiming at disentangling the instrumental profile broadening
and the relevant X-ray powder diffraction (XRPD) profile shape is presented.
The technique consists of three steps: denoising by means of wavelet
transforms, background suppression by morphological functions and deblurring by
a Lucy--Richardson damped deconvolution algorithm. Real XRPD intensity profiles
of ceria samples are used to test the performances. Results show the robustness
of the method and its capability of efficiently disentangling the instrumental
broadening affecting the measurement of the intrinsic physical line profile.
These features make the whole procedure an interesting and user-friendly tool
for the pre-processing of XRPD data.
|
0502582v2
|
2005-03-31
|
Bistability and Hysteresis in the Sliding Friction of a Dimer
|
The sliding friction of a dimer moving over a periodic substrate and
subjected to an external force is studied in the steady state for arbitrary
temperatures within a one-dimensional model. Nonlinear phenomena that emerge
include dynamic bistability and hysteresis, and can be related to earlier
observations for extended systems such as the Frenkel-Kontorova model. Several
observed features can be satisfactorily explained in terms of the resonance of
a driven-damped nonlinear oscillator. Increasing temperature tends to lower the
resonant peak and wash out the hysteresis.
|
0503725v1
|
2005-04-01
|
Exact coherent states of a harmonically confined Tonks-Girardeau gas
|
Using a scaling transformation we exactly determine the dynamics of an
harmonically confined Tonks-Girardeau gas under arbitrary time variations of
the trap frequency. We show how during a one-dimensional expansion a
``dynamical fermionization'' occurs as the momentum distribution rapidly
approaches an ideal Fermi gas distribution, and that under a sudden change of
the trap frequency the gas undergoes undamped breathing oscillations displaying
alternating bosonic and fermionic character in momentum space. The absence of
damping in the oscillations is a peculiarity of the truly Tonks regime.
|
0504024v2
|
2005-04-28
|
Non-equilibrium coherence dynamics of a soft boson lattice
|
We study the non-equilibrium evolution of the phase coherence of a
Bose-Einstein condensate (BEC) in a one dimensional optical lattice, as the
lattice is suddenly quenched from an insulating to a superfluid state. We
observe slowly damped phase coherence oscillations in the regime of large
filling factor (~100 bosons per site) at a frequency proportional to the
generalized Josephson frequency. The truncated Wigner approximation (TWA)
predicts the frequency of the observed oscillations.
|
0504762v2
|
2005-05-18
|
Spin Dynamics in the Two-Dimensional Spin 1/2 Heisenberg Antiferromagnet
|
We present low-temperature dynamic properties of the quantum two-dimensional
antiferromagnetic Heisenberg model with spin S=1/2. The calculation of the
dynamic correlation function is performed by combining a projection operator
formalism and the modified spin-wave theory (MSW), which gives a gap in the
dispersion relation for finite temperatures. The so calculated dynamic
correlation function shows a double peak structure.We also obtain the spin-wave
damping and compare our results to experimental data and to theoretical results
obtained by other authors using different approaches.
|
0505458v1
|
2005-05-30
|
Emergence and decay of turbulence in stirred atomic Bose-Einstein condensates
|
We show that a `weak' elliptical deformation of an atomic Bose-Einstein
condensate rotating at close to the quadrupole instability frequency leads to
turbulence with a Kolmogorov energy spectrum. The turbulent state is produced
by energy transfer to condensate fragments that are ejected by the quadrupole
instability. This energy transfer is driven by breaking the two-fold rotational
symmetry of the condensate. Subsequently, vortex-sound interactions damp the
turbulent state leading to the crystalization of a vortex lattice.
|
0505730v1
|
2005-06-07
|
Clustering in mixing flows
|
We calculate the Lyapunov exponents for particles suspended in a random
three-dimensional flow, concentrating on the limit where the viscous damping
rate is small compared to the inverse correlation time. In this limit Lyapunov
exponents are obtained as a power series in epsilon, a dimensionless measure of
the particle inertia. Although the perturbation generates an asymptotic series,
we obtain accurate results from a Pade-Borel summation. Our results prove that
particles suspended in an incompressible random mixing flow can show pronounced
clustering when the Stokes number is large and we characterise two distinct
clustering effects which occur in that limit.
|
0506175v1
|
2005-06-16
|
Interferometric Time-Resolved Probing of Acoustic Modes in Single Gold Nanospheres
|
We measure the transient absorption of single gold particles with a
common-path interferometer. The prompt electronic part of the signal provides
high-contrast images for diameters as small as 10 nm. Mechanical vibrations of
single particles appear on a longer timescale (period of 16 ps for 50 nm
diameter). They reveal the full heterogeneity of the ensemble, and the
intrinsic damping of the vibration. We also observe a lower-frequency mode
involving shear. Ultra-fast pump-probe spectroscopy of individual particles
opens new insight into mechanical properties of nanometer-sized objects.
|
0506401v1
|
2005-06-16
|
Unexpected Density Fluctuations in Jammed Disordered Sphere Packings
|
We computationally study jammed disordered hard-sphere packings as large as a
million particles. We show that the packings are saturated and hyperuniform,
i.e., that local density fluctuations grow only as a logarithmically-augmented
surface area rather than the volume of the window. The structure factor shows
an unusual non-analytic linear dependence near the origin, $S(k)\sim|k|$. In
addition to exponentially damped oscillations seen in liquids, this implies a
weak power-law tail in the total correlation function, $h(r)\sim-r^{-4}$, and a
long-ranged direct correlation function.
|
0506406v1
|
2005-07-27
|
Population inversion of driven two-level systems in a structureless bath
|
We derive a master equation for a driven double-dot damped by an unstructured
phonon bath, and calculate the spectral density. We find that bath mediated
photon absorption is important at relatively strong driving, and may even
dominate the dynamics, inducing population inversion of the double dot system.
This phenomenon is consistent with recent experimental observations.
|
0507638v2
|
2005-08-07
|
Ultrafast light-induced magnetization dynamics in ferromagnetic semiconductors
|
We develop a theory of the magnetization dynamics triggered by ultrafast
optical excitation of ferromagnetic semiconductors. We describe the effects of
the strong carrier spin relaxation on the nonlinear optical response by using
the Lindblad semigroup method. We demonstrate magnetization control during
femtosecond timescales via the interplay between circularly polarized optical
excitation, hole-spin damping, polarization dephasing, and the Mn-hole spin
interactions. Our results show a light-induced magnetization precession and
relaxation for the duration of the optical pulse.
|
0508178v1
|
2005-09-14
|
Dissipation through spin Coulomb drag in electronic spin dynamics
|
Spin Coulomb drag (SCD) constitutes an intrinsic source of dissipation for
spin currents in metals and semiconductors. We discuss the power loss due to
SCD in potential spintronics devices and analyze in detail the associated
damping of collective spin-density excitations. It is found that SCD
contributes substantially to the linewidth of intersubband spin plasmons in
parabolic quantum wells, which suggests the possibility of a purely optical
quantitative measurement of the SCD effect by means of inelastic light
scattering.
|
0509362v1
|
2005-09-15
|
Granular dynamics in compaction and stress relaxation
|
Elastic and dissipative properties of granular assemblies under uniaxial
compression are studied both experimentally and by numerical simulations.
Following a novel compaction procedure at varying oscillatory pressures, the
stress response to a step-strain reveals an exponential relaxation followed by
a slow logarithmic decay. Simulations indicate that the latter arises from the
coupling between damping and collective grain motion predominantly through
sliding. We characterize an analogous "glass transition" for packed grains,
below which the system shows aging in time-dependent sliding correlation
functions.
|
0509416v1
|
2005-10-05
|
Staggered Ladder Spectra
|
We exactly solve a Fokker-Planck equation by determining its eigenvalues and
eigenfunctions: we construct nonlinear second-order differential operators
which act as raising and lowering operators, generating ladder spectra for the
odd and even parity states. These are staggered: the odd-even separation
differs from even-odd. The Fokker-Planck equation describes, in the limit of
weak damping, a generalised Ornstein-Uhlenbeck process where the random force
depends upon position as well as time. Our exact solution exhibits anomalous
diffusion at short times and a stationary non-Maxwellian momentum distribution.
|
0510113v1
|
2005-10-07
|
RSFQ devices with selective dissipation for quantum information processing
|
We study the possibility to use frequency dependent damping in RSFQ circuits
as means to reduce dissipation and consequent decoherence in RSFQ/qubit
circuits. We show that stable RSFQ operation can be achieved by shunting the
Josephson junctions with an $RC$ circuit instead of a plain resistor. We derive
criteria for the stability of such an arrangement, and discuss the effect on
decoherence and the optimisation issues. We also design a simple flux generator
aimed at manipulating flux qubits.
|
0510189v1
|
2005-10-21
|
Proca equation for laser pulses interaction with matter
|
In this paper the interaction of ultrashort laser pulses with matter is
investigated. The scattering and potential motion of heat carriers, as well as
the external force are considered. It is shown that the heat transport is
described by the Proca equation. For thermal Heisenberg type relation V\tau ~
\hbar, (\tau is the relaxation time and V is the potential) the solution of the
Proca equation (PR) are the distortionless damped wave equation.
Key words: Ultrashort laser pulses; Quantum heat transport equation; Proca
thermal equation.
|
0510578v1
|
2005-11-17
|
Attophysics of Thermal Phenomena in Carbon Nanotubes
|
In this paper heat transport in carbon nanotubes is investigated. When the
dimension of the structure is of the order of the de Broglie wave length
transport phenomena must be analysed by quantum mechanics. In this paper we
derived the Dirac type thermal equation .The solution of the equation for the
temperature fields for electrons can either be damped or can oscillate
depending on the dynamics of the scattering. Key words: Carbon nanotubes,
ultrashort laser pulses, Dirac thermal equation, temperature fields.
|
0511445v1
|
2005-12-14
|
Terahertz plasma wave generation in ultra-short-channel Field Effect Transistors: theory vs experiment
|
Taking into account both the scattering and the velocity saturation of
carriers, we examine the "shallow-water" instability of the two-dimensional
electron gas in a field effect transistor. It is shown that both the scattering
(which is analogous to friction in a shallow-water channel) and the carrier
velocity saturation lead to damping of the plasma wave instability. Threshold
diagram of instability is calculated. The actual device parameters required for
observation of plasma wave generation are compared with those reported in
recent sub-terahertz emission experiments.
|
0512322v1
|
2006-01-18
|
Brownian Dynamics, Time-averaging and Colored Noise
|
We propose a method to obtain the equilibrium distribution for positions and
velocities of a one-dimensional particle via time-averaging and Laplace
transformations. We apply it to the case of a damped harmonic oscillator in
contact with a thermal bath. The present method allows us to treat, among other
cases, a Gaussian noise function exponentially correlated in time, e.g.,
Gaussian colored noise. We obtain the exact equilibrium solution and study some
of its properties.
|
0601419v2
|
2006-02-01
|
Special frequencies in reflection spectra of Bragg multiple quantum well structures
|
We have studied theoretically optical reflection spectra from the Bragg
multiple quantum well structures. We give an analytical explanation of the
presence of two special frequencies in the spectra at which the reflection
coefficient weakly depends on the quantum well number. The influence of the
exciton nonradiative damping on the reflection spectra has been analyzed. It
has been shown that allowance for the dielectric contrast gives rise to the
third special frequency at which the contributions to the reflectivity related
to the dielectric contrast and the exciton resonance mutually compensate one
another.
|
0602013v1
|
2006-02-03
|
Low Ghz loss in sputtered epitaxial Fe
|
We show that sputtered, pure epitaxial iron films can have high-frequency
loss as low as, or lower than, any known metallic ferromagnetic
heterostructure. Minimum 34 Ghz ferromagnetic resonance (FMR) linewidths of 41
Oe are demonstrated, some ~ 5-10 % lower than the previous minimum reported for
molecular beam epitaxially (MBE) deposited Fe. Intrinsic and extrinsic damping
have been separated over 0-40 Ghz, giving a lower bound for intrinsic LL(G)
relaxation rates of lambda or G = 85 MHz (alpha = 0.0027) and extrinsic 50 Mhz.
Swept frequency measurements indicate the potential for integrated frequency
domain devices with Q>100 at 30-40 Ghz.
|
0602094v1
|
2006-02-04
|
Spin-transfer-driven ferromagnetic resonance of individual nanomagnets
|
We demonstrate a technique that enables ferromagnetic resonance (FMR)
measurements of the normal modes for magnetic excitations in individual
nanoscale ferromagnets, smaller in volume by a factor of 1000 than can be
probed by other methods. The measured peak shapes indicate two regimes of
response: simple FMR and phase locking. Studies of the resonance frequencies,
amplitudes, and linewidths as a function of microwave power, DC current, and
magnetic field provide detailed new information about the exchange, damping,
and spin-transfer torques that govern the dynamics in magnetic nanostructures.
|
0602105v1
|
2006-02-10
|
Low-frequency vortex dynamic susceptibility and relaxation in mesoscopic ferromagnetic dots
|
Vortex dynamics in a restricted geometry is considered for a magnetic system
consisting of ferromagnetic cylindrical dots. To describe the vortex dynamic
susceptibility and relaxation the equation of motion for the vortex center
position is applied. The dependencies of the vortex dynamic susceptibility and
resonance linewidth on geometrical parameters are calculated. A new method of
extracting damping parameter from the vortex low-frequency resonance peaks is
proposed and applied for interpretation of resonance data on FeNi circular
dots.
|
0602279v1
|
2006-03-09
|
High Frequency dynamics in metallic glasses
|
Using Inelastic X-ray Scattering we studied the collective dynamics of the
glassy alloy Ni$_{33}$Zr$_{67}$ in the first pseudo Brillouin zone, an
energy-momentum region still unexplored in metallic glasses. We determine key
properties such as the momentum transfer dependence of the sound velocity and
of the acoustic damping, discussing the results in the general context of
recently proposed pictures for acoustic dynamics in glasses. Specifically, we
demonstrate the existence in this strong glass of well defined (in the Ioffe
Regel sense) acoustic-like excitations well above the Boson Peak energy.
|
0603251v1
|
2006-03-13
|
Synchronization in the BCS Pairing Dynamics as a Critical Phenomenon
|
Fermi gas with time-dependent pairing interaction hosts several different
dynamical states. Coupling between the collective BCS pairing mode and
individual Cooper pair states can make the latter either synchronize or
dephase. We describe transition from phase-locked undamped oscillations to
Landau-damped dephased oscillations in the collisionless, dissipationless
regime as a function of coupling strength. In the dephased regime, we find a
second transition at which the long-time asymptotic pairing amplitude vanishes.
Using a combination of numerical and analytical methods we establish a
continuous (type II) character of both transitions.
|
0603317v1
|
2006-04-04
|
Reshaping-induced spatiotemporal chaos in driven, damped sine-Gordon systems
|
Spatiotemporal chaos arising from the competition between
sine-Gordon-breather and kink-antikink-pair solitons by reshaping an ac force
is demonstrated. After introducing soliton collective coordinates, Melnikov's
method is applied to the resulting effective equation of motion to estimate the
parameter-space regions of the ac force where homoclinic bifurcations are
induced. The analysis reveals that the chaos-order threshold exhibits
sensitivity to small changes in the force shape. Computer simulations of the
sine-Gordon system show good agreement with these theoretical predictions.
|
0604081v1
|
2006-04-10
|
Anomalous Diffusion of Inertial, Weakly Damped Particles
|
The anomalous (i.e. non-Gaussian) dynamics of particles subject to a
deterministic acceleration and a series of 'random kicks' is studied. Based on
an extension of the concept of continuous time random walks to
position-velocity space, a new fractional equation of the Kramers-Fokker-Planck
type is derived. The associated collision operator necessarily involves a
fractional substantial derivative, representing important nonlocal couplings in
time and space. For the force-free case, a closed solution is found and
discussed.
|
0604245v1
|
2006-05-08
|
Microscopic Calculation of Spin Torques in Disordered Ferromagnets
|
Effects of conduction electrons on magnetization dynamics, represented by
spin torques, are calculated microscopically in the first order in spatial
gradient and time derivative of magnetization. Special attention is paid to the
so-called $\beta$-term and the Gilbert damping, $\alpha$, in the presence of
electrons' spin-relaxation processes, which are modeled by quenched magnetic
(and spin-orbit) impurities. The obtained results such as $\alpha \ne \beta$
hold for localized as well as itinerant ferromagnetism.
|
0605186v1
|
2006-05-12
|
Magnetic properties of spin-orbital polarons in lightly doped cobaltates
|
We present a numerical treatment of a spin-orbital polaron model for
Na_xCoO_2 at small hole concentration (0.7 < x < 1). We demonstrate how the
polarons account for the peculiar magnetic properties of this layered compound:
They explain the large susceptibility; their internal degrees of freedom lead
both to a negative Curie-Weiss temperature and yet to a ferromagnetic
intra-layer interaction, thereby resolving a puzzling contradiction between
these observations. We make specific predictions on the momentum and energy
location of excitations resulting from the internal degrees of freedom of the
polaron, and discuss their impact on spin-wave damping.
|
0605334v1
|
2006-07-13
|
Hydrodynamics of Superfluid Bose Gases in an Optical Lattice at Finite Temperatures
|
Starting from an effective action for the order parameter field, we derive a
coupled set of generalized hydrodynamic equations for a Bose condensate in an
optical lattice at finite temperatures. Using the linearized hydrodynamic
equations, we study the microscopic mechanism of the Landau instability due to
the collisional damping process between condensate and noncondensate atoms. It
is shown that the Landau criterion of the superfluidity for the uniform system
is modified due to the presence of the periodic optical lattice potential.
|
0607320v1
|
2006-07-31
|
Inhomogeneous losses and complexness of wave functions in chaotic cavities
|
In a two-dimensional microwave chaotic cavity ohmic losses located at the
contour of the cavity result in different broadenings of different modes. We
provide an analytic description and establish the link between such an
inhomogeneous damping and the complex (non-real) character of biorthogonal wave
functions. This substantiates the corresponding recent experimental findings of
Barthelemy et al. [Europhys. Lett. 70, 162 (2005)].
|
0607810v2
|
2006-08-05
|
Disruption of reflecting Bose-Einstein condensates due to inter-atomic interactions and quantum noise
|
We perform fully three-dimensional simulations, using the truncated Wigner
method, to investigate the reflection of Bose-Einstein condensates from abrupt
potential barriers. We show that the inter-atomic interactions can disrupt the
internal structure of a cigar-shaped cloud with a high atom density at low
approach velocities, damping the center-of-mass motion and generating vortices.
Furthermore, by incorporating quantum noise we show that scattering halos form
at high approach velocities, causing an associated condensate depletion. We
compare our results to recent experimental observations.
|
0608135v3
|
2006-08-08
|
Intraplanar Magnetic Excitations in Na0.5CoO2: An Inelastic Neutron Study
|
Inelastic neutron scattering measurements mapping the in-plane magnetic
interactions of Na0.5CoO2 reveal dispersive excitations at points above an
energy gap Eg = 11.5(5) meV at the superstructural Bragg reflections. The
excitations are highly damped, broadening with increasing energy, and disappear
at hw ~ 35 meV, a strong indication that the magnetism is itinerant. Tilting
into the ac plane reduces the value of Eg by 25%, suggesting that the
dispersion along c is significant and the magnetic correlations are
three-dimensional, as seen at the higher doping levels.
|
0608196v2
|
2006-08-11
|
Perturbation theory for localized solutions of sine-Gordon equation: decay of a breather and pinning by microresistor
|
We develop a perturbation theory that describes bound states of solitons
localized in a confined area. External forces and influence of inhomogeneities
are taken into account as perturbations to exact solutions of the sine-Gordon
equation. We have investigated two special cases of fluxon trapped by a
microresistor and decay of a breather under dissipation. Also, we have carried
out numerical simulations with dissipative sine-Gordon equation and made
comparison with the McLaughlin-Scott theory. Significant distinction between
the McLaughlin-Scott calculation for a breather decay and our numerical result
indicates that the history dependence of the breather evolution can not be
neglected even for small damping parameter.
|
0608263v1
|
2006-08-11
|
Motion of a sphere in an oscillatory boundary layer: an optical tweezer based study
|
The drag forces acting on a single polystyrene sphere in the vicinity of an
oscillating glass plate have been measured using an optical tweezer. The phase
of the sphere is found to be a sensitive probe of the dynamics of the sphere.
The evolution of the phase from an inertially-coupled regime to a purely
velocity-coupled regime is explored. Moreover, the frequency dependent response
is found to be characteristic of a damped oscillator with an effective inertia
which is several orders of magnitude greater than that of the particle.
|
0608281v1
|
2006-08-26
|
Ab initio simulations of excited carrier dynamics in carbon nanotubes
|
Combining time-dependent density functional calculations for electrons with
molecular dynamics simulations for ions, we investigate the dynamics of excited
carriers in a (3,3) carbon nanotube at different temperatures. Following an
hv=6.8 eV photoexcitation, the carrier decay is initially dominated by
efficient electron-electron scattering. At room temperature, the excitation gap
is reduced to nearly half its initial value after ~230 fs, where coupling to
phonons starts dominating the decay. We show that the onset point and damping
rate in the phonon regime change with initial ion velocities, a manifestation
of temperature dependent electron-phonon coupling.
|
0608580v1
|
2006-09-12
|
Colloidal transport through optical tweezer arrays
|
Viscously damped particles driven past an evenly spaced array of potential
energy wells or barriers may become kinetically locked in to the array, or else
may escape from the array. The transition between locked-in and free-running
states has been predicted to depend sensitively on the ratio between the
particles' size and the separation between wells. This prediction is confirmed
by measurements on monodisperse colloidal spheres driven through arrays of
holographic optical traps.
|
0609276v1
|
2006-09-13
|
Laser-like Instabilities in Quantum Nano-electromechanical Systems
|
We discuss negative damping regimes in quantum nano-electromechanical systems
formed by coupling a mechanical oscillator to a single-electron transistor
(normal or superconducting). Using an analogy to a laser with a tunable
atom-field coupling, we demonstrate how these effects scale with system
parameters. We also discuss the fluctuation physics of both the oscillator and
the single-electron transistor in this regime, and the degree to which the
oscillator motion is coherent.
|
0609329v2
|
2006-10-21
|
Boson-controlled quantum transport
|
We study the interplay of collective dynamics and damping in the presence of
correlations and bosonic fluctuations within the framework of a newly proposed
model, which captures the principal transport mechanisms that apply to a
variety of physical systems. We establish close connections to the transport of
lattice and spin polarons, or the dynamics of a particle coupled to a bath. We
analyse the model by exactly calculating the optical conductivity, Drude
weight, spectral functions, groundstate dispersion and particle-boson
correlation functions for a 1D infinite system.
|
0610592v2
|
2006-11-27
|
Microscopic Calculation of Spin Torques and Forces
|
Spin torques, that is, effects of conduction electrons on magnetization
dynamics, are calculated microscopically in the first order in spatial gradient
and time derivative of magnetization. Special attention is paid to the
so-called \beta-term and the Gilbert damping, \alpha, in the presence of
electrons' spin-relaxation processes, which are modeled by quenched magnetic
impurities. Two types of forces that the electric/spin current exerts on
magnetization are identified based on a general formula relating the force to
the torque.
|
0611669v1
|
2007-01-11
|
The Shear Viscosity to Entropy Density Ratio of Trapped Fermions in the Unitarity Limit
|
We extract the shear viscosity to entropy density ratio \eta/s of cold
fermionic atoms in the unitarity limit from experimental data on the damping of
collective excitations. We find that near the critical temperature \eta/s is
roughly equal to 1/2 in units of \hbar/k_B. With the possible exception of the
quark gluon plasma, this value is closer to the conjectured lower bound
1/(4\pi) than any other known liquid.
|
0701251v4
|
2007-01-18
|
High energy kink in the single particle spectra of the two-dimensional Hubbard model
|
Employing dynamical cluster quantum Monte Carlo calculations we show that the
single particle spectral weight A(k,w) of the one-band two-dimensional Hubbard
model displays a high energy kink in the quasiparticle dispersion followed by a
steep dispersion of a broad peak similar to recent ARPES results reported for
the cuprates. Based on the agreement between the Monte Carlo results and a
simple calculation which couples the quasiparticle to spin fluctuations, we
conclude that the kink and the broad spectral feature in the Hubbard model
spectra is due to scattering with damped high energy spin fluctuations.
|
0701429v1
|
2007-01-18
|
Quantum vortices in optical lattices
|
A vortex in a superfluid gas inside an optical lattice can behave as a
massive particle moving in a periodic potential and exhibiting quantum
properties. In this Letter we discuss these properties and show that the
excitation of vortex motions in a two-dimensional lattice can lead to striking
measurable changes in its dynamic response. It would be possible by means of
Bragg spectroscopy to carry out the first direct measurement of the effective
vortex mass, the pinning to the underlying lattice, and the dissipative
damping.
|
0701439v1
|
2007-01-23
|
Resonant spin polarization and spin current in a two-dimensional electron gas
|
We study the spin polarization and its associated spin-Hall current due to
EDSR in disordered two-dimensional electron systems. We show that the disorder
induced damping of the resonant spin polarization can be strongly reduced by an
optimal field configuration that exploits the interference between Rashba and
Dresselhaus spin-orbit interaction. This leads to a striking enhancement of the
spin susceptibility while the spin-Hall current vanishes at the same time. We
give an interpretation of the spin current in geometrical terms which are
associated with the trajectories the polarization describes in spin space.
|
0701559v2
|
2007-01-26
|
Casimir force driven ratchets
|
We explore the non-linear dynamics of two parallel periodically patterned
metal surfaces that are coupled by the zero-point fluctuations of the
electromagnetic field between them. The resulting Casimir force generates for
asymmetric patterns with a time-periodically driven surface-to-surface distance
a ratchet effect, allowing for directed lateral motion of the surfaces in
sizeable parameter ranges. It is crucial to take into account inertia effects
and hence chaotic dynamics which are described by Langevin dynamics. Multiple
velocity reversals occur as a function of driving, mean surface distance, and
effective damping. These transport properties are shown to be stable against
weak ambient noise.
|
0701641v1
|
2007-01-31
|
Elementary Electronic Excitations in Graphene Nanoribbons
|
We analyze the collective mode spectrum of graphene nanoribbons within the
random phase approximation. In the undoped case, only metallic armchair
nanoribbons support a propagating plasmon mode. Landau damping of this mode is
shown to be suppressed through the chirality of the single particle
wavefunctions. We argue that undoped zigzag nanoribbons should not support
plasmon excitations because of a broad continuum of particle-hole excitations
associated with surface states, into which collective modes may decay. Doped
nanoribbons have properties similar to those of semiconductor nanowires,
including a plasmon mode dispersing as $q\sqrt{-\ln qW}$ and a static
dielectric response that is divergent at $q=2k_F$.
|
0701787v1
|
2007-02-05
|
Diffusion in Modulated Media
|
We study the motion of Brownian particle in modulated media in the strong
damping limit by using {\em toy model}, with special emphasis on the transition
from localise to diffusive behavior. By using model potential we have seen the
localised behavior when the number of minima of the potential is finite in the
asymptotic time limit. In the limit of infinite number of minima we have seen
the diffusive behavior.We calculate exactly the diffusion coefficient in
periodic field of force. We have also studied the transport in commensurate and
incommensurate media.
|
0702092v1
|
2007-02-08
|
Nonequilibrium fluctuation induced escape from a metastable state
|
Based on a simple microscopic model where the bath is in a non-equilibrium
state we study the escape from a metastable state in the over-damped limit.
Making use of Fokker-Planck-Smoluchowski description we derive the time
dependent escape rate in the non-stationary regime in closed analytical form
which brings on to fore a strong non-exponential kinetic of the system mode.
|
0702217v1
|
2007-02-09
|
Dissipation peak as an indicator of sample inhomogeneity in solid $^4$He oscillator experiments
|
A simple phenomenological model is developed for the recent torsional
oscillator experiments on solid $^4$He. Within this model, for a homogeneous
sample there is a specific quantitative relation between the change in the
oscillator's frequency and its maximum damping at the apparent supersolid
transition. Much of the published data do not satisfy this relation, indicating
that the dissipation peaks in those samples are strongly inhomogeneously
broadened.
|
0702243v2
|
2007-03-06
|
Controllable Josephson-Like Tunneling in Two-Component Bose-Einstein Condensates Coupled with Microwave via Feshbach Resonance and Trapping Potential
|
We put forward a scheme for controlling Josephson-like tunneling in
two-component Bose-Einstein condensates coupled with microwave field via
Feshbach resonance and tuning aspect ratio of trapping potential. We prove how
to realize a perfect periodic oscillation from a fast damped and irregular
oscillation on relative number of atoms in future experiment. In particular,
intensity of Josephson-like tunneling can be successfully controlled through
controlling speed of recovering the initial value of intra-atomic interaction
and aspect ratio of trapping potential. Interestingly, we find that relative
number of atoms represents two different types of oscillation in respond to
periodic modulation of attractive intra-atomic interaction.
|
0703160v1
|
2007-03-09
|
Phase Transition in a Two-level-cavity System in an Ohmic Environment
|
We propose that in the presence of an Ohmic, de-phasing type environment, a
two-level-cavity system undergoes a quantum phase transition from a state with
damped Rabi oscillation to a state without. We present the phase diagram and
make predictions for pump and probe experiment. Such a strong coupling effect
of the environment is beyond the reach of conventional perturbative treatment.
|
0703238v1
|
2007-03-13
|
The Resonant Light Absorption by Semiconductor Quantum Dots
|
The cross section of light absorption by semiconductor quantum dots in the
case of the resonance with excitons $\Gamma_6 \times \Gamma_7$ in cubical
crystals $T_d$ is calculated. It is shown that an interference of stimulating
and induced electric and magnetic fields must be taken into account. The
absorption section is proportional to the exciton nonradiative damping
$\gamma$.
|
0703324v2
|
2007-03-13
|
Internal Josephson-Like Tunneling in Two-Component Bose-Einstein Condensates Affected by Sign of the Atomic Interaction and External Trapping Potential
|
We study the Josephson-like tunneling in two-component Bose-Einstein
condensates coupled with microwave field in respond to various attractive and
repulsive atomic interaction under the various aspect ratio of trapping
potential and the gravitational field. It is very interesting to find that the
dynamic of Josephson-like tunneling can be controlled from fast damped
oscillations and asymmetric occupation to nondamped oscillation and symmetric
occupation.
|
0703327v1
|
1994-04-26
|
Semiclassical Gravitational Effects in de Sitter Space at Finite Temperature
|
In the framework of finite temperature conformal scalar field theory on de
Sitter space-time the linearized Einstein equations for the renormalized stress
tensor are exactly solved. In this theory quantum field fluctuations are
concentrated near two spheres of the de Sitter radius, propagating as light
wave fronts. Related cosmological aspects are shortly discussed. The analysis,
performed for flat expanding universe, shows exponential damping of the
back-reaction effects far from these spherical objects. The obtained solutions
for the semiclassical Einstein equations in de Sitter background can be
straightforwardly extended also to the anti-de Sitter geometry.
|
9404048v1
|
1996-07-31
|
Cosmological Perturbations of Ultrarelativistic Plasmas
|
Scalar cosmological perturbations of a weakly self-interacting plasma mixed
with a perfect radiation fluid are investigated. Effects of this plasma are
considered through order $\lambda^{3/2}$ of perturbative thermal-field-theory
in the radiation dominated universe. The breakdown of thermal perturbation
theory at vastly subhorizon scales is circumvented by a Pad\'e approximant
solution. Compared to collisionless plasmas the phase speed and subhorizon
damping of the plasma density perturbations are changed. An example for a
self-interacting thermal field is provided by the neutrinos with effective
4-fermion interactions.
|
9607077v1
|
1996-10-22
|
A detailed study of quasinormal frequencies of the Kerr black hole
|
We compute the quasinormal frequencies of the Kerr black hole using a
continued fraction method. The continued fraction method first proposed by
Leaver is still the only known method stable and accurate for the numerical
determination of the Kerr quasinormal frequencies. We numerically obtain not
only the slowly but also the rapidly damped quasinormal frequencies and analyze
the peculiar behavior of these frequencies at the Kerr limit. We also calculate
the algebraically special frequency first identified by Chandrasekhar and
confirm that it coincide with the $n=8$ quasinormal frequency only at the
Schwarzschild limit.
|
9610048v1
|
1996-10-25
|
Cosmological Gravitational Wave in a Gravity with Quadratic Order Curvature Couplings
|
We present a set of equations describing the cosmological gravitational wave
in a gravity theory with quadratic order gravitational coupling terms which
naturally arise in quantum correction procedures. It is known that the
gravitational wave equation in the gravity theories with a general $f(R)$ term
in the action leads to a second order differential equation with the only
correction factor appearing in the damping term. The case for a $R^{ab} R_{ab}$
term is completely different. The gravitational wave is described by a fourth
order differential equation both in time and space. However, curiously, we find
that the contributions to the background evolution are qualitatively the same
for both terms.
|
9610059v1
|
1996-12-16
|
Evolutionary Dynamics While Trapped in Resonance: A Keplerian Binary System Perturbed by Gravitational Radiation
|
The method of averaging is used to investigate the phenomenon of capture into
resonance for a model that describes a Keplerian binary system influenced by
radiation damping and external normally incident periodic gravitational
radiation. The dynamical evolution of the binary orbit while trapped in
resonance is elucidated using the second order partially averaged system. This
method provides a theoretical framework that can be used to explain the main
evolutionary dynamics of a physical system that has been trapped in resonance.
|
9612040v1
|
1998-01-09
|
Spacetime foam as a quantum thermal bath
|
An effective model for the spacetime foam is constructed in terms of nonlocal
interactions in a classical background. In the weak-coupling approximation, the
evolution of the low-energy density matrix is determined by a master equation
that predicts loss of quantum coherence. Moreover, spacetime foam can be
described by a quantum thermal field that, apart from inducing loss of
coherence, gives rise to effects such as gravitational Lamb and Stark shifts as
well as quantum damping in the evolution of the low-energy observables.
|
9801024v2
|
1998-02-09
|
Viscoelastic effects in a spherical Gravitational Wave antenna
|
Internal friction effects are responsible for line widening of the resonance
frequencies in spherical gravitational wave detectors, and result in
exponentially damped oscillations of its eigenmodes with a decay time which is
proportional to the quality factor of the mode and to its inverse frequency. We
study the solutions to the equations of motion for a viscoelastic spherical GW
detector based on various different assumptions about the material's
constituent equations. Quality factor dependence on mode frequency is
determined in each case, and a discussion of its applicability to actual
detectors is made.
|
9802018v1
|
1998-06-09
|
Thermal properties of spacetime foam
|
Spacetime foam can be modeled in terms of nonlocal effective interactions in
a classical nonfluctuating background. Then, the density matrix for the
low-energy fields evolves, in the weak-coupling approximation, according to a
master equation that contains a diffusion term. Furthermore, it is argued that
spacetime foam behaves as a quantum thermal field that, apart from inducing
loss of coherence, gives rise to effects such as gravitational Lamb and Stark
shifts as well as quantum damping in the evolution of the low-energy
observables. These effects can be, at least in principle, experimentally
tested.
|
9806047v2
|
1998-06-26
|
Chaos in the Kepler System
|
The long-term dynamical evolution of a Keplerian binary orbit due to the
emission and absorption of gravitational radiation is investigated. This work
extends our previous results on transient chaos in the planar case to the three
dimensional Kepler system. Specifically, we consider the nonlinear evolution of
the relative orbit due to gravitational radiation damping as well as external
gravitational radiation that is obliquely incident on the initial orbital
plane. The variation of orbital inclination, especially during resonance
capture, turns out to be very sensitive to the initial conditions. Moreover, we
discuss the novel phenomenon of chaotic transition.
|
9806107v1
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1998-10-26
|
Formation of a rotating hole from a close limit head-on collision
|
Realistic black hole collisions result in a rapidly rotating Kerr hole, but
simulations to date have focused on nonrotating final holes. Using a new
solution of the Einstein initial value equations we present here waveforms and
radiation for an axisymmetric Kerr-hole-forming collision starting from small
initial separation (the ``close limit'' approximation) of two identical
rotating holes. Several new features are present in the results: (i) In the
limit of small separation, the waveform is linear (not quadratic) in the
separation. (ii) The waveforms show damped oscillations mixing quasinormal
ringing of different multipoles.
|
9810080v1
|
1998-11-09
|
Quantum Gravity effects near the null black hole singularity
|
The structure of the Cauchy Horizon singularity of a black hole formed in a
generic collapse is studied by means of a renormalization group equation for
quantum gravity. It is shown that during the early evolution of the Cauchy
Horizon the increase of the mass function is damped when quantum fluctuations
of the metric are taken into account.
|
9811026v2
|
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